1. Field of the Invention
The present invention relates to an image processing method and an image processing apparatus, and more particularly to an image processing method and an image processing apparatus for performing a correction process to image data such as a digital photographic image or the like.
2. Related Background Art
In recent years, with the advance of inkjet printing technology, a printout image more excellent than conventional one can be obtained by using a high-pixel digital camera and printing technology such as an inkjet printing system.
However, in case of printing out a digitalized photographic image, there are problems to be improved in quality of the image to be output. With respect to the problems, as one of the cause, it is considered that color balance for an entire image is disordered due to, e.g., an overexposure state or an underexposure state of the image, or a phenomenon so-called “color fog”.
For example, in case of performing automatic photographing using a camera, since AE (automatic exposure) is functioned, if the blue sky is contained in the most part of a background, an underexposure photographing state of inviting a dark scene is provided, thereby resulting in a state that a subject is taken in an unexcellent state.
As an example of a digital camera, since an image is taken by a CCD (charge coupled device) camera, a color of a wavelength not visible to human eyes is also captured as an image. Then, when a signal containing that color information is processed as signals R (red), G (green) and B (blue) (or R, G and B signals), the color not be naturally recognized by the human eyes becomes visible color, thereby sometimes resulting in an unsuitable color balance. In this case, although a process of cutting infrared rays by using a filter is performed, this process is not always perfect measures. Furthermore, a color correction balance is limited by a method of a real-time correction. As a result, a perfect process is hard to be performed, and an entire color balance is not often perfectly ensured.
Such disorder in color balance on a taken image gives an influence to a print image as a result. Therefore, in order to obtain an excellent printed out result, it is desirable to correct an input image itself, such as a taken image or the like, to an image of having suitable color balance.
As a method of performing this correction, the present inventor proposed a method of setting a correction condition on the basis of the highest brightness or the lowest brightness obtained by analyzing a histogram of an image, in Japanese Patent Application No. 10-177272 (corresponding to U.S. patent application Ser. No. 09/337,548 filed on Jun. 22, 1999).
Incidentally, the following problem other than the “color fog” or the color balance disorder depends on the exposure is found in quality of an image to be printed.
As described above, with the advance of the inkjet printing technology in recent years, dots formed by ink are minimized to level of exceeding a visible limit, and printing of “nongranular state” can be realized. In this point, the inkjet printing technology is almost equal to printing technology of a silver bromide photograph. However, according to a characteristic of ink used in the inkjet printing, there has been remained a problem that an absolute density realized in a print image is lower than that of the silver bromide photograph as shown in FIG. 20.
It should be noted that this problem is not peculiar to the inkjet printing technology, but the similar problem is found in another printing system or a display such as a CRT (cathode ray tube) or the like. Generally, it has been known that an output image becomes clear by properly increasing the density, and an excellent color image properly reproduced can be obtained.
If the density is uniformly increased for the purpose of increasing density of an output image, gradation of a dark part is crushed or broken in an image having lots of dark parts. As a result, image quality is sometimes deteriorated.